Metal electrodes composed of a metal base, such as titanium and tantalum, having coatings of mixed metal oxides, especially of metals of the platinum group, have been known for some time (see, e.g., South African Pat. No. 68/7482). Such electrodes, being resistant to attack under electrolysis conditions, are dimensionally stable and permit construction of electrolytic cells having higher capacity and reduced electrical energy requirements. For these reasons, they have found wide use in the production of alkali metal hydroxide and chlorine by electrolysis of salt brine. Numerous variations of dimensionally stable metal electrodes have been patented and have been described in the literature. For example, G. Bianchi has investigated discharge of chlorine by brine electrolysis employing platinum and platinum alloy electrodes, especially platinum/iridium electrodes, as well as metallic electrodes coated with metallic oxides, especially those coated with oxides of ruthenium, iridium and titanium [J. Appl. Electrochem. 1 (1971) 231-243]. Atanasoski et al. investigated oxygen evolution reaction on titanium-based platinum/iridium-catalyzed dimensionally stable anodes and concluded that such anodes have smaller polarization than metals commonly used as catalysts in oxygen evolution [J. Appl. Electrochem. 5 (1975 ) 159-163]. German Offenlegungschrift No. 2,045,348 describes titanium-based metal electrodes having an active coating of a solid solution of titanium dioxide and at least one dioxide of chromium, manganese and/or rhenium. Metal electrodes containing a conductive coating incorporating tellurium together with other coating substances are described in German Offenlegungscrhift No. 2,136,391 and 2,136,394.
It is an object of the present invention to provide conductive coatings for metal electrodes having improved catalytic activity for oxygen generation in electrochemical processes.
It is another object of the present invention to provide such coatings for electrodes for use in electrochemical processes involving oxidation of organic compounds.
It is a further object of the present invention to provide electrodes for electrochemical processes having enhanced catalytic activity for oxygen evolution in electrochemical processes in both acidic and alkaline media.